Rock type based free water level inversion

Abstract

A determination of the free water level for a hydrocarbon-bearing reservoir is provided that accounts for the different classified rock types (that is, facies) in the reservoir. The free water level for each unique combination of facies is determined using a least squares minimization between a reference bulk volume of oil (Bvolog) determined from well logs a bulk volume of oil (Bvocalc) calculated from a saturation height function for each of the facies present in the reservoir. Systems and process for determining the free water level are provided.

Description

BACKGROUNDField of the Disclosure[0001]Embodiments of the disclosure generally relate to the production of hydrocarbons from hydrocarbon-bearing reservoirs and, more particularly, to the evaluation of fluids in such reservoirs.Description of the Related Art[0002]Information about fluids in a hydrocarbon-bearing reservoir are important for properly characterizing the reservoir and conducting optimal drilling and production operations to efficiently extract hydrocarbons. Increasing the accuracy of this information may increase the accuracy of subsequent determinations used to characterize a reservoir. Various devices and techniques exist for determining the fluids information, such as downhole tools and core sampling of reservoir rock. These techniques have particular limitations and costs and may not provide the most accurate fluids information. Moreover, the determination of some fluids information may be time-consuming and may result in delays in drilling and production.SUMMARY[000...

AI Technical Summary

Benefits of technology

[0008]FIG. 5 is a bar graph 500 of the heights of free water level (HFWL) obtained by the existing error minimization techniques using seven different rock types. The bar graph 500 includes the free water level heights from rock type 1 (corresponding to the best quality rock) and rock type 7 (corresponding to the lowest quality rock). The bar graph also includes the free water level height for the combination of all rock types. As shown in FIG. 5, the free water level heights have a difference of 75 feet relative to the different rock types and show a relatively large degree of variability. These large differences in the determined free water levels can have a great impact on reservoir management and reserves estimation, especially in large fields where even small inaccuracies in the free water level could translate into large amounts of hydrocarbon volume in place (HCPV).

Problems solved by technology

These techniques have particular limitations and costs and may not provide the most accurate fluids information.

Moreover, the determination of some fluids information may be time-consuming and may result in delays in drilling and production.

However, this technique is limited to fields that have no prior production and wells having intervals that contain water and hydrocarbons.

The error minimization routine is typically interval-based and does not account for the different rock types that may or may not be present in the considered interval.

As many different rock types existing in a reservoir, an approach where an inversion is based on an entire interval can produce large errors and large differences.

Such errors may be greater in heterogeneous reservoirs having regions with different rock types in every well.

As shown in FIG. 6, the technique results in a high variability in the free water level height in a reservoir due to the variation in rock qualities and distance from the free water level.

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